Herpesvirus ateles (HVA) and Herpesvirus saimiri (HVS) have been found to transform marmoset monkey T\lymphocytes leading to permanently established lymphoid cell lines. We have recently demonstrated that continuously growing HVA/HVS-transformed T-cell lines have the capacity to kill certain tumor-derived target cells in a short-term 51Cr release assay in vitro. Progress to date indicates that HVA/HVS-transformed cytotoxic cell lines correspond to marmoset natural killer (NK) cells and that their activity is subject to the same regulatory mechanisms as that of marmoset NK cells. The present investigation aims at further characterization of HVA/HVS cell-line-mediated cytotoxicity and determining if this reactivity may be used as a general model system to study lymphocytotoxic mechanisms. Among the questions to be approached: Is the lytic mechanism and its regulation displayed by HVA/HVS cell lines representative of that (or those) used by normal cells? Do effector cell receptors and target antigens reflect naturally occurring receptors or antigens? Can transformed cell lines be established which express other cell-mediated immune functions as well as antigen specificity? Specifically, the cytotoxicity mechanism expressed by HVA/HVS-transformed cell lines will be characterized and compared to nontransformed effector cells with regard to target cell specificity and influences of various inhibitors, mediators, and inducers. Attempts will be made to clone HVA/HVS cytotoxic cells and prepare monoclonal antibodies against effector cell receptors involved in recognition and cytotoxicity. Other possible cell-mediated functions (helper or suppressor activity) will be determined, and the creation of antigen-specific functional cell lines will be investigated. These results will be used to ascertain the relevance of this system for the study of lymphocytotoxic mechanisms and its significance for cellular immune function.